Increasingly stringent regulations for two-stroke engines necessitate a reduction in emissions. Emissions reduction techniques have so far included engine calibration strategies using injection timing to minimize lost fuel at the expense of mixture preparation and power. Traditional calibration strategies for reducing emissions focus on timing the Start of Injection (SOI) to minimize the amount of lost fuel. Since injection occurs during cylinder scavenging, the path the fuel cloud takes is strongly influenced by the scavenging pattern produced by the transfer ports. The flow pattern which provides good power performance in carbureted engines also convects fuel spray toward the exhaust port in the direct injection engine. These fuel losses can be minimized by allowing less time for the scavenging flows to convect fuel to the exhaust port. However, this strategy also reduces the amount of time for the fuel spray to mix with the air delivered during scavenging resulting in a reduced power output.
It would be desirable to further reduce these fuel losses out of the exhaust port without excessively degrading mixture preparation and trapped oxygen. It is therefore desirable to optimize the scavenging pattern to maximize fuel trapping without sacrificing mixture preparation.
It would be desirable to have a two-stroke, direct injection, internal combustion engine with reduced emissions, increased power output and improved fuel economy. It would also be desirable to achieve these results without increasing the size of the bore, bore spacing or stroke of the engine compared to that of current generation engines in order to remain within the current constraints of cost, weight, commonality, and engine envelope targets.